Toshiba TV29C90 problem; Image fades to black...

[Dave D]

"Robert Morein" <nowhere@nothing.com> wrote in message
news:4ECdnXNN2sqp8LuiXTWJjA@comcast.com...

<<snipped>>

In my experience with 12V fans,

They're 5V fans.

a series resistor works nicely, as does
running them from a stiff 6V supply.

A series resistor generates heat, diodes drop voltage and run cooler.. They
can be soldered into the fan leads then covered with heatshrink sleeving. A
6V supply will speed these fans up.

Unless you have something unusual, these fans do vary RPM in response to
power supply voltage.

You will have to determine the resistor by trial and error, since the fans
do not respond linearly to voltage.

Silicon diodes in series allow small increments and an easier way to select
the required speed.

BTW, you replied to my post, I did not post the query Maybe your news
service isn't showing all the posts?

Dave

 

[Bushy]

All I do is throw another log on the fire!

Beats an electric kettle any day!

Peter

 

[Dave D]

"Sam Goldwasser" <sam@saul.cis.upenn.edu> wrote in message
news:6wy8yhs5yi.fsf@saul.cis.upenn.edu...

"Dave D" <someone@somewhere.com> writes:

A series resistor generates heat, diodes drop voltage and run cooler..
They
can be soldered into the fan leads then covered with heatshrink
sleeving. A
6V supply will speed these fans up.

Not quite. If you have a voltage drop and current flow, you have IV=P
generates the same heat. Doesn't matter if it is a diode or a resistor.
The difference is that the power dissipation is roughly proportional to
current rather than a square function because the voltage drop is more or
less constant.

Exactly, so the diode will run cooler, like I said Naturally, the losses
are to heat, I didn't mean that diodes magically dump the energy into a
black hole!

Dave

 

[A E]

Dave D wrote:

"A E" <aeisenhut@videotron.ca> wrote in message
news:3F268E42.A0D93AD2@videotron.ca...
Dave D wrote:

"Robert Morein" <nowhere@nothing.com> wrote in message
news:4ECdnXNN2sqp8LuiXTWJjA@comcast.com...

snipped

In my experience with 12V fans,

They're 5V fans.

a series resistor works nicely, as does
running them from a stiff 6V supply.

A series resistor generates heat, diodes drop voltage and run cooler..
They

So, you're saying with the same VI, a diode generates less heat than a
resistor???????????


Nope, see Sam's post. It will always drop a relatively fixed voltage,
regardless of current draw, so it is more efficient than a resistor in this
application.

Dave

Makes no sense. You will simply not draw more current through that diode than
with a resistor, because the load is the same... If you put a resistor in series
with the fan, and the resistor happens to drop .6V (simple to figure out, if you
can draw a load line, otherwise a bit of experimenting), the same amount of
current will go through that resistor as through a diode... Same heat
dissipation in both cases. Don't you think?

 

[A E]

Dave D wrote:

"Sam Goldwasser" <sam@saul.cis.upenn.edu> wrote in message
news:6wy8yhs5yi.fsf@saul.cis.upenn.edu...
"Dave D" <someone@somewhere.com> writes:

A series resistor generates heat, diodes drop voltage and run cooler..
They
can be soldered into the fan leads then covered with heatshrink
sleeving. A
6V supply will speed these fans up.

Not quite. If you have a voltage drop and current flow, you have IV=P
generates the same heat. Doesn't matter if it is a diode or a resistor.
The difference is that the power dissipation is roughly proportional to
current rather than a square function because the voltage drop is more or
less constant.


Exactly, so the diode will run cooler, like I said Naturally, the losses

It'll only run cooler than a resistor in the case of increasing the input
voltage to the fan-diode combination, but then, the fan starts to run faster,
which is goes against what the OP wants, so it's no longer doing its job!
Therefore, it's not efficient. So you add another diode to drop the extra
voltage, and guess what, you're back to dissipating the same as a resistor...
"Efficient" would be if the diode did the same thing as a resistor dropping .6V,
while dissipating less heat, which it doesn't. Given an input voltage, a given
fan, and a given target of reduced RPM, and you only have diodes and resistors
to do it with, you'll dissipate the *same* amount of heat in either case.
There's no 'efficiency' to using a diode... You *will* have to drop the *same*
voltage with either a resistor or a chain of diodes, and the current will be the
same in both cases. There's no magic about this. P=VI.

 

Leonard G. Caillouet <lcaillo_ns_@devoynet.com> wrote:
: No chain. We are a one store operation. The position is likely best for a
: young person getting started due to the physical nature of the install work
: and the point in the growth of the shop at this time. The amount of service
: work that I can provide is maybe half-time, so we will share this person
: with the install side. We like this combination to give the tech a good
: idea of the application end of the equipment and giving our install dept a
: more technical capability. Eventually, this person could make some decent
: money. First year expect ~$24K depending on ability.

Great way to start out (I did it this way).

Now I'm an engineer at one of those "big computer companies".

I still remember the old job and enjoyed it immensely.

b.

 

[Andre]

"Dave D" <someone@somewhere.com> wrote in message news:<bg600r$9eq$1@titan.btinternet.com>...

"Robert Morein" <nowhere@nothing.com> wrote in message
news:4ECdnXNN2sqp8LuiXTWJjA@comcast.com...

snipped

In my experience with 12V fans,

They're 5V fans.

a series resistor works nicely, as does
running them from a stiff 6V supply.

A series resistor generates heat, diodes drop voltage and run cooler.. They
can be soldered into the fan leads then covered with heatshrink sleeving. A
6V supply will speed these fans up.

I tried running the unit off 4.5 V and it works - but almost no torque .

Unless you have something unusual, these fans do vary RPM in response to
power supply voltage.

You will have to determine the resistor by trial and error, since the fans
do not respond linearly to voltage.



Silicon diodes in series allow small increments and an easier way to select
the required speed.

Interesting idea - thanks

BTW, you replied to my post, I did not post the query Maybe your news
service isn't showing all the posts?

Dave

 

[Bob Minchin]

Tom Jacobs wrote:

"Chris" <chris@ross-engineering.fsnet.co.uk> wrote in message
news:3f26346b$1@nntp.onyx.net


"James Sweet" <jamessweet@hotmail.com> wrote in message
news:M0XUa.160597$N7.21682@sccrnsc03...
: These must be european washing machines, or perhaps very high end ones in
: north america. Every washing machine I've ever seen inside of uses a 1/2hp
: capacitor start AC induction motor with two separate windings for high and

I have just changed my 18 year old "hoover computer control" machine just
for a new "LG". The Hoover motor had Brushes and what sounded and appeared
to be Thyristor controller it seemed very sophisticated and reliable for an
old washer. Chris R

Hi All,
I've recently ripped apart 4 front loaders purchased in the U/K within
the last 5 years. Thay all seem to be of Italian origin, 2 had
commutator
motors and 2 had induction motors (capacitor run, I think, no
centrifugal
switches could be heard). I have had all of these running successfully,
and fukky understand the tacho' run type of speed control on comm mtors.
However, the induction motors (2 speed), also have a tacho fitted at the
rear, and a small control box. These 2 run very well at both speeds
direct
from the mains, with the cap connected. Does anyone know what the taco'
bit is for ?.
1 more question for those more enlightened than myself, the induction
motors are marked with conflicting current / wattage ratings, ie

220/240 V, 4 A, 330 W or similar. Can someone please explain ?

Besr Regards

Tom.

"Nunce excreta in extractum est".

--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG

Current rating will be the current drawn from the supply, power will be the power
output of the motor. The difference will be shared between power factor and the
motor efficiency.

Tacho (you eat tacos !!) on and induction motor?? Hmm! I wonder. Perhaps some form
of electronic switching of start winding/capacitor perhaps.

Bob

 

[CWatters]

I'm with you AE on this one. Same voltage drop * same current = same power.

If that's too much power (unlikely) then then the only way to beat this is
to use a digital speed controller (eg PWM).


"A E" <aeisenhut@videotron.ca> wrote in message
news:3F26BD02.E7260E5@videotron.ca...

Dave D wrote:

"A E" <aeisenhut@videotron.ca> wrote in message
news:3F268E42.A0D93AD2@videotron.ca...
Dave D wrote:

"Robert Morein" <nowhere@nothing.com> wrote in message
news:4ECdnXNN2sqp8LuiXTWJjA@comcast.com...

snipped

In my experience with 12V fans,

They're 5V fans.

a series resistor works nicely, as does
running them from a stiff 6V supply.

A series resistor generates heat, diodes drop voltage and run
cooler..
They

So, you're saying with the same VI, a diode generates less heat than a
resistor???????????


Nope, see Sam's post. It will always drop a relatively fixed voltage,
regardless of current draw, so it is more efficient than a resistor in
this
application.

Dave

Makes no sense. You will simply not draw more current through that diode
than
with a resistor, because the load is the same... If you put a resistor in
series
with the fan, and the resistor happens to drop .6V (simple to figure out,
if you
can draw a load line, otherwise a bit of experimenting), the same amount
of
current will go through that resistor as through a diode... Same heat
dissipation in both cases. Don't you think?

 

[cpemma]

A E wrote:

Dave D wrote:

a series resistor works nicely, as does
running them from a stiff 6V supply.

A series resistor generates heat, diodes drop voltage and run
cooler.. They

So, you're saying with the same VI, a diode generates less heat
than a resistor???????????


Nope, see Sam's post. It will always drop a relatively fixed
voltage, regardless of current draw, so it is more efficient than a
resistor in this application.

Dave

Makes no sense. You will simply not draw more current through that
diode than with a resistor, because the load is the same... If you
put a resistor in series with the fan, and the resistor happens to
drop .6V (simple to figure out, if you can draw a load line,
otherwise a bit of experimenting), the same amount of current will go
through that resistor as through a diode... Same heat dissipation in
both cases. Don't you think?

The major drawback with resistors is that the v drop depends on current, and
at start-up current is high, so v drop is high - the supply is anything but
"stiff". Aiming for say 7v on a 12v fan, the fan may not even get going.
Diodes drop a fairly steady voltage over the range of fan currents likely.

 

[Nigel Eaton]

In article <f27773661e71601191fabc7a65ea0678.72682@mygate.mailgate.org>,
Tom Jacobs <tomjacobs@lineone.net> writes

and fukky understand the tacho'

I ruv you rong time, ten dorrah!

Sorry, it *had* to be done...
--
Nigel

When the only tools you have are a Bridgeport, a Myford, a Colchester and
assorted other stuff, every problem looks like a steam engine.

 

[Jeff]

"Lenny" <captainvideo462002@yahoo.com> wrote in message
news:d980bc2c.0307281750.f8bbfc4@posting.google.com...

My son who works with me in my electronics service business is
presently enrolled in an Electronics Technology course at the local
College. I introduced him to test equipment by getting him a used 260
and a new cheapo hand held digital from Harbor Freight, just so that
he could "get his feet wet". He's a hard worker, and a good boy and
now I would like to do something special for him. He has asked for a
Fluke portable meter with a case for his birthday. Although I own
older model Fluke and HP bench meters, I rarely have a need for them
in my work so with the large selection of new Fluke portables
available frankly I'm stumped as the what is the best deal on a decent
service meter for the money. Thanks for any advice. Lenny Stein.

Lenny you realy did not say what type of work your
son will be using the meter for, and that would help
a lot in choosing one.
But the 20, 70, 80 series are good meters.
Jeff

 

[Sam Goldwasser]

One thing to note: In order to guarantee that the fan starts with a series
resistor, a large electrolytic cap (e.g., 500 uF) should be placed across
the resistor or diode(s). Then, power will initially be applied at
full voltage long enough to get it going.

A typical 12 V 3-1/2" fan will run just above stall speed with a 200 ohm
resistor in series to 12 V. I've built regulated temperature controllers
by using the speed range from this to full speed in a feedback loop.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the Feedback Form at repairfaq.org. Thanks.

 

[Marko]

BG: OK let's give it a try. This time I will get it right about where the
guides are

Originally this machine had four guides:
(1) one solidly affixed to left of erase head
(2) one on left of record head, but affixed to the transport frame
(3) One spot welded to the right side of the record head
(4) One affixed (with miniature screw) to left side of PB head

The one on the right side of the record head is less than a cm from the
guide on the left of the PB head (PB head guide is effectively missing, not
repairable, mangled)

As far as stability of the tape going across the heads goes, I feel that
the 3 remaining guides will be enough, if they are aligned

The two problems are as follows:

(1) The guide to the left of the record head is affixed to frame and all
other guides must correspond to this one or the tape will not ride smoothly
on the heads.

(2) Seems like the guide to the right of the record head should not effect
the path of the tape over the PB head because it is over the screw that is
not for adjustment (the mounting screw that is tightened and not
adjustable). BUT, it does because I didn't notice the 3rd head when I was
adjusting the azimuth for the record head (I thought it was the playback
head at the time). Turning the azimuth adjustment for the record head
affects the path of the tape over the PB head. I recall seeing the PB
amplitude vary on a scope as the azimuth screw for Rec head was turned.

I hope I have written this in a readable manner.

All I can see is that I should adjust the Rec and PB heads over and over
until hopefully they are aligned.

Any ideas or warnings, BG? Thanks for your help. Your advice has given me
a much needed understanding of this situation. Mark
"bg" <bg@nospam.com> wrote in message
news:bg68j6$bkg$1@terabinaries.xmission.com...

Just about every deck I've ever seen has a guide on the ingoing side of
the
erase head and a guide on the outgoing side of the playback head, with no
other guides in between. It is also common practise to affix the guides to
the heads, not the chassis. On the chassis there will be posts that hold
the shell in place, they are not tape guides.
I have plenty of time . If you are ready to continue let me know
bg
Marko wrote in message ...
BG: I have reread your post several times and now realize that without
the
guide on the PB head then it is up to me and luck to get it going right.

Unless you have some more advice, thanks much, you've been a great help.
Sincerely, Mark

"bg" <bg@nospam.com> wrote in message
news:bg3s50$qi0$1@terabinaries.xmission.com...
The heads from left to right are, the erase head, the record head and
the
playback head. Any cassette I've ever seen has a guide attached to the
playback head. If possible, bend the damaged guide back into place.
Usually
this guide is spot welded, therefore the height of the guide might not
have
changed. This guide sets the tracking which usually is not adjustable
because the guide is fixed to the playback head at the factory. On rare
occasions this guide is adjustable.
The tilt of the head sets azimuth which is adjustable on all decks. You
will
have to examine the record and playback heads to see if there is
azimuth
adjustments for both heads. I would expect there is. Head height raises
or
lowers the position of the head gaps on the tape. Azimuth rotates the
gaps
so that they are aligned perpendicular (90 degrees) to the tape.
Azimuth
will have a slight effect on the head height. Another head adjustment
you
might have is zenith. Usually located at the rear of the head, it
tilts
the
face of the head, so that the head is parallel to the tape. This
adjustment
if incorrect, would tilt the top of the head either closer or further
from
the tape than the bottom of the head. It causes uneven head wear and it
causes the tape to scew up and down. As the tape scews, the azimuth and

tracking will also be out of adjustment. The erase head should also
have
a
non adjustable guide affixed to it.
Check to see that you have these guides in place, the azimuth and
zenith
adjustments, and that the adjustments will move the heads. If you can't
physically align the heads, or the guides are bad, there is no sense in
going any further. you will have to replace whatever mechanics are bad.
You might want to sacrafice an old cassette by cutting away the plastic
shell in the area where the heads contact the tape. This will give you
the
abiltiy to see how the tape rides over the heads. If the tape is
visibly
moving up or down, you will have to correct this. It is impossible to
align
a head to tape that moves all over the place. The basic concept is to
set
all guides at the same height so that the tape enters the shell and
leaves
the shell at the same height. Any guides in between should not raise or
lower the tape as it travels thru the shell.
Post back here with your results and we'll determine the next step.
bg


Marko wrote in message ...
BG: I thought I would check for replies just one more time before I
stopped
NG activity for awhile. Glad I did.


I have a signal generator, alignment tape, scope, and HP5210 freq
meter
that
I have used to set the motor RPM with 1KHz test tone.

I haven't checked yet, but I am hoping that

(1) the head on the far right is the play head
(2) the tape monitor switch will allow me to record a test tone (I
will
use
10KHz) and then monitor it with the play head so that I can align the
record
head.
(3) that the tape guide on the PB head (which has been bent out of the
tape
path) is not necessary for proper tape transfer over the heads.

What worries me is that the tape guide is on the record head and I
must
align the playback head first.

I didn't notice the third head at first and aligned the playback with
the
record head adjustment screw. This worked because the tape guide is
on
the
record head.

How do I start out with proper alignment of the two tape guides before
aligning the heads? One guide, the first one, is affixed to the
transport
frame and the second guide is affixed to the record head. I think
this
problem may have been encountered by
whoever worked on it before it was sent to a resale shop. I could see
that
they had disturbed the paint on the screws. It also had two stretched
belts
and a very dirty rec/play switch on the board, so I'm not sure. The
belts
may have stretched and the grease in the switch may have dried from
sitting
on the shelf for years after they encountered the alignment problem.

What do you suggest? Sincerely, Mark (this is a top post)






----- Original Message -----
From: "bg" <bg@nospam.com
Newsgroups: sci.electronics.repair
Sent: Sunday, July 27, 2003 11:46 PM
Subject: Re: Fisher cassette heads


You need an audio generator, and an AC audio voltmeter with a DB
scale.
If
you have this equipment I'll steer you through it.
bg
Marko wrote in message ...
I have a Fisher cassette deck with separate record and playback
heads.
I
assume that the one in the middle, the large one, is the record
head.

I have a professional alignment tape. How does one align the
record
head?
There is a tape monitor switch which probably is used to compare
input
to
output.

These are ferrite heads with no visible wear, new belts, switches
cleaned
thoroughly: this deck is worth an alignment as opposed to the trash
can
(mabey).

Also, one tape guide (the one on the far left, just to the left of
the
record head) is affixed to the transport frame. The second guide
is
affixed
to the record head. The third tape guide on the playback head is
bent
over
to the side, obviously bent intentionally to get it out of the way.
The
adjustment screw to this bent guide is not accessable for
adjustment
(sloppy
design). The third tape guide is probably not necessary since it
is
only
about a cm from the guide on the record head. This transport may
be
a
piece
of junk due to lousy design.

Any helpful hints will be appreciated Thanks, Mark





"bg" <bg@nospam.com> wrote in message
news:bg29k2$6ia$1@terabinaries.xmission.com...
You need an audio generator, and an AC audio voltmeter with a DB
scale.
If
you have this equipment I'll steer you through it.
bg
Marko wrote in message ...
I have a Fisher cassette deck with separate record and playback
heads.
I
assume that the one in the middle, the large one, is the record
head.

I have a professional alignment tape. How does one align the
record
head?
There is a tape monitor switch which probably is used to compare
input
to
output.

These are ferrite heads with no visible wear, new belts, switches
cleaned
thoroughly: this deck is worth an alignment as opposed to the trash
can
(mabey).

Also, one tape guide (the one on the far left, just to the left of
the
record head) is affixed to the transport frame. The second guide
is
affixed
to the record head. The third tape guide on the playback head is
bent
over
to the side, obviously bent intentionally to get it out of the way.
The
adjustment screw to this bent guide is not accessable for
adjustment
(sloppy
design). The third tape guide is probably not necessary since it
is
only
about a cm from the guide on the record head. This transport may
be
a
piece
of junk due to lousy design.

Any helpful hints will be appreciated Thanks, Mark

 

[Dave D]

"A E" <aeisenhut@videotron.ca> wrote in message
news:3F26D621.DE75419@videotron.ca...

Andre wrote:


Silicon diodes in series allow small increments and an easier way to
select
the required speed.

Interesting idea - thanks

Except it does nothing more than a resistor, and a 0.6V drop at a supply
of 5V gives you 12%
increments, hardly small.
I'd stick with a resistor, or go the PWM way, that's the right way to do
it.

I don't think PWM is the right way to drive an electronic brushless motor,
unless the pwm waveform is converted to a dc level with a capacitor. PWM is
a great way to drive a brush motor, I don't think it would have a desirable
effect on a brushless one, it may even damage the circuitry in the fan.

Your claim that a diode does nothing more than a resistor is not true. It
provides a (approx) 0.6V drop without reducing the available current
significantly, not the same as a resistor at all. A resistor will have a far
greater effect on startup torque and running torque than a diode.

Anyway, the best way to control one of these brushless motors IMO is a LM317
or similar
regulator with a pot so the OP can set the exact speed he wants. Not the
simplest way but a sure way of getting the speed right.

Dave

 

[EsMot]

I wouldn't mix diodes and resistors when it's about voltage drop... You're
right about P=V*I, what you forgot is that P also equals R*I2.... Now: go
and measure the diode's resistance and do this calculation for the same
voltage drop and the same current as your resistance. You'll then see the
difference. Apply any voltage acros the resistor the current is goind to be
V/R. Do the same thing with the diode: it won't last long, first of all, but
if you keep the voltage in reasonable limits so you won't exceed the maximum
current of the diode you'll see that there's a differnt relationship between
voltage and current and it's definitely non linear. The resistor is a
component with high (I mean from a bit more than a copper wire to something
that one might consider an insulator) resistance while the diode drops
voltage because of the P-N junction polarization voltage. Think of the P-N
junction as an insulator (which it really is, even if it's called
"semiconductor") which starts leaking electrons in a direction if properly
polarized. If the voltage across the diode is less than 0.6V for Si and 0.3V
for Ge the diode acts like an insulator. It won't open at all because the
electric field acros the P-N junction is not strong enough to free
electrons. If the voltage goes over the above mentioned values some elctrons
are freed (remember that the main, only and single difference between
conductors and insulators is the status of electrons inside it...) and it
turns into a conductor. That 0.6 to 0.7 volts remains constant no matter the
current passing through the diode. The ideal diode won't drop more than 0.6
volts, the real diode drops a bit more because other than the semiconductor
effect the P-N junctions has it's own internal resistance (imagine it as an
ideal diode series with a tiny resistor). Anyway, the internal resistance is
much lower than that of a resistor you would use for the same purpose, if
you don't exceed the rated current of the diode you can consider it's
resistance "zero".
We can now return to our problem: first of all I never tried to reduce speed
of a brushless motor... I must admit I never thought of it. The PC power
supply fans are sometimes quite noisy, the processor fans are really good, I
don't remember one noisy enough to make me want to lower the rpm. I also
believe that 12V motors are easier to control than 5V anyway, you can drop
the voltage quite a lot until you reach the point where the transistors
won't polarize any more. What would a capacitor do in parallel with a hall
sensor? In a brushless motor a hall sensor is used to determine the position
of magnetic poles of the rotor and trigger the energization of the
corresponding coil to create the spinning magnetic field. This scheme
simulates the comutator and brushes in a nomal motor motor. What you can try
is to insert a little diode series with each coil inside the motor. You'll
keep the same polarization voltage for the control circuits so you'll still
have the transistors properly polarized, but the voltage on each coil is
going to be 0.7V lower which will result in a lower torque. Or you may try a
resistor... If you have enough room inside, of course (I don't think so).
But I think that'll do the trick. Good luck!

SM


"A E" <aeisenhut@videotron.ca> wrote in message
news:3F26D621.DE75419@videotron.ca...

Andre wrote:


Silicon diodes in series allow small increments and an easier way to
select
the required speed.

Interesting idea - thanks

Except it does nothing more than a resistor, and a 0.6V drop at a supply
of 5V gives you 12%
increments, hardly small.
I'd stick with a resistor, or go the PWM way, that's the right way to do
it.

 

[bg]

It sounds as though you have enough guides to make it work.
Alignment tapes are usually full track. You can't set tracking with it but
you can use it for azimuth. Hopefully the fixed guides are in the right
position. My gut feel is that the azimuth would be the only adjustment you
need to make unless the guides were moved somehow.
The normal method for setting the head height is to record a tone on the
tape and then measure the track positions with a toolmakers microscope. I'm
sure you don't have this equipment, so the next best thing would be to
record a 1000 hz tone on a known good cassette deck and use that tape as
your tracking standard. As you play the tape back in the Fisher deck,
lightly push or lift the playback head to see if the playback level
increases. If the guide on your playback head hasn't been moved, your
tracking should be OK. Flip the tape over and check the levels again. For
every .001 inch that the tracking is off, you lose about .4db of signal
level. If the levels are within 1/2 to 1 db from side one, you probably
won't be able to improve the tracking by moving the playback head guide.
Moving it that small amount would be very difficult, and the guides have to
be wider than the tape by about .001 inch to allow the tape to fit thru it
anyway. So .001 of tape movement is perfectly normal.
To set azimuth on the playback head, use the 10 khz tone on your alignment
tape. There's two ways to do this. One way is to simply adjust your playback
head azimuth for maximum output at 10 khz. The other method is to measure
the phase between the left and right tracks. (lissajous patterns)
Set up your scope for X-Y mode. Plug the left line out into one channel and
the right line out into the other channel. When the two tracks are in
perfect phase alignment, the scope trace should make a line angled at 45
degrees . It looks like this -- (/) .
If the phase alignment is out by 180 degrees the line is angled like
this ---- (\). Between 0 and 180 degrees the line changes to an oval or a
circle. Multiples of 360 degrees will look like it's in phase alignment, but
the length of the line will get shorter. So what you want is the longest
line possible angled like (/). Note that when the azimuth is off, the level
of the 10 khz tone drops off. Lower frequencies are barely affected by bad
azimuth, that's why it is set using a higher frequency tone. If the 45
degree line fluctuates rapidly, there is a problem with the tape moving up
and down. This might be due to the guides not all being at the same height
or bad zenith. Your alignment tape might be stretched also. It doesn't take
very much abuse to stretch a tape. If the tape seems to be bad , try
recording a 10k tone on a good cassette deck and use that for your alignment
tape.
Now that the playback head is in correct azimuth and height. You can align
your record head to your playback head. Check the height of the record head
by recording a 1000 hz tone. Move the record head up or down until you get
maximum output from the playback head. Again, if you flip the tape over, the
levels should playback within about 1db. seeing as the record head has a
guide welded to it , there should be no reason for the record head tracking
to be incorrect. Set the azimuth by recording a 10khz tone and adjust the
record head azimuth for maximum output from the playback head or 0 degree
phase shift between left and right outputs.
You might need to set levels, EQ, bias, and calibrate the VU meters. This
would be hard to do unless the adjustment pots are marked on the circuit
board, but not impossible to figure out.
Let me know how you make out.


Marko wrote in message ...

BG: OK let's give it a try. This time I will get it right about where the
guides are

Originally this machine had four guides:
(1) one solidly affixed to left of erase head
(2) one on left of record head, but affixed to the transport frame
(3) One spot welded to the right side of the record head
(4) One affixed (with miniature screw) to left side of PB head

The one on the right side of the record head is less than a cm from the
guide on the left of the PB head (PB head guide is effectively missing, not
repairable, mangled)

As far as stability of the tape going across the heads goes, I feel that
the 3 remaining guides will be enough, if they are aligned

The two problems are as follows:

(1) The guide to the left of the record head is affixed to frame and all
other guides must correspond to this one or the tape will not ride smoothly
on the heads.

(2) Seems like the guide to the right of the record head should not effect
the path of the tape over the PB head because it is over the screw that is
not for adjustment (the mounting screw that is tightened and not
adjustable). BUT, it does because I didn't notice the 3rd head when I was
adjusting the azimuth for the record head (I thought it was the playback
head at the time). Turning the azimuth adjustment for the record head
affects the path of the tape over the PB head. I recall seeing the PB
amplitude vary on a scope as the azimuth screw for Rec head was turned.

I hope I have written this in a readable manner.

All I can see is that I should adjust the Rec and PB heads over and over
until hopefully they are aligned.

Any ideas or warnings, BG? Thanks for your help. Your advice has given me
a much needed understanding of this situation. Mark
"bg" <bg@nospam.com> wrote in message
news:bg68j6$bkg$1@terabinaries.xmission.com...
Just about every deck I've ever seen has a guide on the ingoing side of
the
erase head and a guide on the outgoing side of the playback head, with no
other guides in between. It is also common practise to affix the guides
to
the heads, not the chassis. On the chassis there will be posts that hold
the shell in place, they are not tape guides.
I have plenty of time . If you are ready to continue let me know
bg
Marko wrote in message ...
BG: I have reread your post several times and now realize that without
the
guide on the PB head then it is up to me and luck to get it going right.

Unless you have some more advice, thanks much, you've been a great help.
Sincerely, Mark

"bg" <bg@nospam.com> wrote in message
news:bg3s50$qi0$1@terabinaries.xmission.com...
The heads from left to right are, the erase head, the record head and
the
playback head. Any cassette I've ever seen has a guide attached to the
playback head. If possible, bend the damaged guide back into place.
Usually
this guide is spot welded, therefore the height of the guide might not
have
changed. This guide sets the tracking which usually is not adjustable
because the guide is fixed to the playback head at the factory. On
rare
occasions this guide is adjustable.
The tilt of the head sets azimuth which is adjustable on all decks.
You
will
have to examine the record and playback heads to see if there is
azimuth
adjustments for both heads. I would expect there is. Head height
raises
or
lowers the position of the head gaps on the tape. Azimuth rotates the
gaps
so that they are aligned perpendicular (90 degrees) to the tape.
Azimuth
will have a slight effect on the head height. Another head adjustment
you
might have is zenith. Usually located at the rear of the head, it
tilts
the
face of the head, so that the head is parallel to the tape. This
adjustment
if incorrect, would tilt the top of the head either closer or further
from
the tape than the bottom of the head. It causes uneven head wear and
it
causes the tape to scew up and down. As the tape scews, the azimuth
and

tracking will also be out of adjustment. The erase head should also
have
a
non adjustable guide affixed to it.
Check to see that you have these guides in place, the azimuth and
zenith
adjustments, and that the adjustments will move the heads. If you
can't
physically align the heads, or the guides are bad, there is no sense
in
going any further. you will have to replace whatever mechanics are
bad.
You might want to sacrafice an old cassette by cutting away the
plastic
shell in the area where the heads contact the tape. This will give you
the
abiltiy to see how the tape rides over the heads. If the tape is
visibly
moving up or down, you will have to correct this. It is impossible to
align
a head to tape that moves all over the place. The basic concept is to
set
all guides at the same height so that the tape enters the shell and
leaves
the shell at the same height. Any guides in between should not raise
or
lower the tape as it travels thru the shell.
Post back here with your results and we'll determine the next step.
bg


Marko wrote in message ...
BG: I thought I would check for replies just one more time before I
stopped
NG activity for awhile. Glad I did.


I have a signal generator, alignment tape, scope, and HP5210 freq
meter
that
I have used to set the motor RPM with 1KHz test tone.

I haven't checked yet, but I am hoping that

(1) the head on the far right is the play head
(2) the tape monitor switch will allow me to record a test tone (I
will
use
10KHz) and then monitor it with the play head so that I can align the
record
head.
(3) that the tape guide on the PB head (which has been bent out of
the
tape
path) is not necessary for proper tape transfer over the heads.

What worries me is that the tape guide is on the record head and I
must
align the playback head first.

I didn't notice the third head at first and aligned the playback with
the
record head adjustment screw. This worked because the tape guide is
on
the
record head.

How do I start out with proper alignment of the two tape guides
before
aligning the heads? One guide, the first one, is affixed to the
transport
frame and the second guide is affixed to the record head. I think
this
problem may have been encountered by
whoever worked on it before it was sent to a resale shop. I could
see
that
they had disturbed the paint on the screws. It also had two
stretched
belts
and a very dirty rec/play switch on the board, so I'm not sure. The
belts
may have stretched and the grease in the switch may have dried from
sitting
on the shelf for years after they encountered the alignment problem.

What do you suggest? Sincerely, Mark (this is a top post)






----- Original Message -----
From: "bg" <bg@nospam.com
Newsgroups: sci.electronics.repair
Sent: Sunday, July 27, 2003 11:46 PM
Subject: Re: Fisher cassette heads


You need an audio generator, and an AC audio voltmeter with a DB
scale.
If
you have this equipment I'll steer you through it.
bg
Marko wrote in message ...
I have a Fisher cassette deck with separate record and playback
heads.
I
assume that the one in the middle, the large one, is the record
head.

I have a professional alignment tape. How does one align the
record
head?
There is a tape monitor switch which probably is used to compare
input
to
output.

These are ferrite heads with no visible wear, new belts, switches
cleaned
thoroughly: this deck is worth an alignment as opposed to the
trash
can
(mabey).

Also, one tape guide (the one on the far left, just to the left of
the
record head) is affixed to the transport frame. The second guide
is
affixed
to the record head. The third tape guide on the playback head is
bent
over
to the side, obviously bent intentionally to get it out of the
way.
The
adjustment screw to this bent guide is not accessable for
adjustment
(sloppy
design). The third tape guide is probably not necessary since it
is
only
about a cm from the guide on the record head. This transport may
be
a
piece
of junk due to lousy design.

Any helpful hints will be appreciated Thanks, Mark





"bg" <bg@nospam.com> wrote in message
news:bg29k2$6ia$1@terabinaries.xmission.com...
You need an audio generator, and an AC audio voltmeter with a DB
scale.
If
you have this equipment I'll steer you through it.
bg
Marko wrote in message ...
I have a Fisher cassette deck with separate record and playback
heads.
I
assume that the one in the middle, the large one, is the record
head.

I have a professional alignment tape. How does one align the
record
head?
There is a tape monitor switch which probably is used to compare
input
to
output.

These are ferrite heads with no visible wear, new belts, switches
cleaned
thoroughly: this deck is worth an alignment as opposed to the
trash
can
(mabey).

Also, one tape guide (the one on the far left, just to the left of
the
record head) is affixed to the transport frame. The second guide
is
affixed
to the record head. The third tape guide on the playback head is
bent
over
to the side, obviously bent intentionally to get it out of the
way.
The
adjustment screw to this bent guide is not accessable for
adjustment
(sloppy
design). The third tape guide is probably not necessary since it
is
only
about a cm from the guide on the record head. This transport may
be
a
piece
of junk due to lousy design.

Any helpful hints will be appreciated Thanks, Mark

 

[Sofie]

Jim Dobsin:
Since not all 2 year old 13" GE televisions are built with the same design
and circuitry, the Model Number would obviously give us an idea about the
specific circuitry in your television.
When you reply with the Model Number, be certain to also INCLUDE your
preliminary technical troubleshooting results...... particularly the main PS
voltage readings, component tests, B+ regulation working?, visual
observations, etc. The more information you can post the more specific
will be the suggestions you receive..... also it will give anyone replying
to you a "calibration" of your technical skills and proper usage of test
equipment so any suggestions you receive will be useful to you.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
-------------------------------


"Jim Dobsin" <booboojimd@yahoo.com> wrote in message
news:47367ee9.0307291717.162d88c0@posting.google.com...

This TV is less than 2 years old and is not used a lot. When turned
on, the screen goes green (with horizontal lines approx 1/2" apart)
You can hear audio and even change channels for about 8 seconds before
it shuts off. Help !!!

 

[EsMot]

Hank,

It's maybe redundant with what Robert said: if you keep the DVD opened and
that big fan blowing into it long enough you'll be probably forced to buy a
new DVD for yours will turn blind... Try to determine which component is
overheating and if possible replace it. Sometimes a capacitor does this, if
in the power module you may end up with a higher (or lower) voltage that may
cause the freeze. Just a guess...

SM


"Hank" <sorry@nogood.com> wrote in message
news:vfecnWnyOOZ_RLiiXTWJhw@speakeasy.net...

I have a Phillips/Magnavox DVD player slightly over a year old that
started
overheating on me and freezing. My temporary (and effective) solution has
been to take of the cover, exposing the top and sides. I have my cd player
on top of it so only the two side are open. I then have placed a small
desktop type personal fan in front of the entertainment center and squewed
the player so that the air will blow thru the player. This has kept it
from
overheating.

I'd like to put a small but quiet fan right up against the side of the
player so that the player can be tucked back into the entertainment center
and I no longer have to have that relatively large 6" fan propped up on a
box in front of my entertainment center. I'd also like for the fan to be
regular a/c so I can plug it into the switched a/c outlet in my receiver.
Any ideas of what kind of fan to buy and where to buy it (hopefully
relatively inexpensively)?
Thanks,
Hank

P.S. The problem does not lie in its proximity to other heat producing
equipment. I've tried taking it out of the entertainment center with the
cover off and it still overheated. It needs the forced air flow. I'm
trying
to avoid buying a new dvd because it works fine with forced air
ventilation.

 

[A E]

Dave D wrote:

I don't think PWM is the right way to drive an electronic brushless motor,
unless the pwm waveform is converted to a dc level with a capacitor. PWM is

A cap is cheap.

a great way to drive a brush motor, I don't think it would have a desirable
effect on a brushless one, it may even damage the circuitry in the fan.

Hm, true.

Your claim that a diode does nothing more than a resistor is not true. It
provides a (approx) 0.6V drop without reducing the available current
significantly, not the same as a resistor at all. A resistor will have a far

True for transient state, but I think that in the steady state, a resistor will
do fine, esp. in this case where the resistor will be small. There's still the
question of the only having 0.6V increments to play with. Unless you put in a
bunch of tunnel diodes, Schottky and Ge diodes for extra increments...

greater effect on startup torque and running torque than a diode.

Hm, yes yes I see now.

Anyway, the best way to control one of these brushless motors IMO is a LM317
or similar
regulator with a pot so the OP can set the exact speed he wants. Not the
simplest way but a sure way of getting the speed right.

Simple enough, though. 5 parts, and we can all agree on that! (input cap, LM317,
output cap, resistor, pot) This is more complex than required. Maybe the OP can
just remove half the fan's blades instead...